An optical microphone device has been known as a fine displacement detection device using a acoustic electric element.
The outline of a conventional device will be described using the optical microphone device as an example of a fine vibration detection device.
The device shown in FIG. 7 has a structure such that a diaphragm 1 vibrating finely by sound or the like is provided in an opening provided in part of a detection device case 7, and a light emitting element 13 and a light receiving element 14 are placed on a substrate 18 placed at a position facing the diaphragm 1.
Also, a blackout wall 15 is provided between the light emitting element 13 and the light receiving element 14 so that incident light from the light emitting element 13 is prevented from directly coming into the light receiving element 14. Due incident light from the light emitting element 13 undergoes a change in the amount of its reflected light coming into the receiving element 14. It is possible to achieve an operation as the optical microphone device by detecting the change in the amount of incident light as an electric signal by the light receiving element 14.
In the device shown in FIG. 8, a condensing lens 16 and a converging lens 17 are provided on an optical path between the light emitting element 13 and the diaphragm 1 and an optical path between the diaphragm 1 and the light receiving element 14, respectively.
By providing the condensing lens 16 and the diverging lens 17, the amount of reflected light from the diaphragm 1 coming into the light receiving element 14 can be increased.
In FIG. 9, a light emitting and receiving element 5 with the light emitting element and the light receiving element combined as one united body in such a manner that a vertical resonator type surface light emitting laser element with the distribution of emitted light intensity being almost uniform on the concentric circle is used as the light emitting element 13, and the light receiving element 14 is placed on the concentric circle so as to surround the light emitting element 13 with the light emitting element 13 situated at the center is used, and a light condensing element 2 converging incident light from the light emitting element 13 and leading the same to the diaphragm 1, and also converging divergent reflected light from the diaphragm 1 and leading the same to the light receiving element 14 is provided on an optical path between the light emitting and receiving element 5 and the diaphragm 1.
A circular surface light emitting laser element is placed at the center of the substrate, and the light receiving element is placed on the concentric circle so as to surround this surface light emitting laser element to fabricate the light emitting and receiving element 5. The surface light emitting laser element generally has a characteristic such that the distribution of emitted light intensity is almost uniform on the concentric circle.
Therefore, emitted light emitted toward the diaphragm 1 at a predetermined angle from the light emitting element 13 placed at the center is reflected on the concentric circle with same intensity. Then, the diaphragm 1 vibrates, whereby the reflection angle is changed, and the light reaches the light receiving element 14 on the concentric circle.
Therefore, by detecting a change in the amount of light received by the light receiving element 14 placed on the concentric circle, the vibration displacement of the diaphragm 1 can be detected.
By employing this structure, not only the amount of incident reflected light can considerably be increased, but also the device can be scaled down.
Problems to be Solved by the Invention
FIG. 10 shows a tunnel diagram of the device of FIG. 7, indicating that the light emitting element 13 and the light receiving element 14 each should be placed at a certain distance a with respect to the blackout wall 15.
Also, in FIG. 9, the light receiving element 14 should be placed on the concentric circle so as to surround the surface light emitting laser element placed at the center of the substrate.
This conventional device for detecting a fine displacement by sound has an disadvantage that since the structure and layout of the light receiving element relative to the light emitting element are limited for securing sufficient light reception sensitivity, it is difficult to simplify light emitting and light receiving element units, and the production step is thus complicated.
Also, if reflected light flux dividing means other than a hologram is used, there arise disadvantages that the number of optical parts is increased and the device is scaled up, and that the alignment of each optical part is complicated and so on.
The present invention has been devised for solving the problems described above, and has as its object the provision of a fine displacement detection device in which a reflected light flux dividing element for dividing converged reflected light is provided between the light condensing element and the light emitting and receiving element, whereby the degree of freedom for the structure and layout of the light receiving element is enhanced, and the step of producing the light emitting and receiving element can be simplified, and the light condensing element is achieved by a micro lens or hologram lens formed on the plane substrate, and the reflected light flux dividing element is achieved by the hologram formed on the plane substrate, whereby the number of optical parts can be reduced and the device can be scaled down, and thus the alignment of each optical part can easily be achieved.